Rubber formulations, either synthetic or naturally occurring, must be processed in order to prepare finished products which are usable in industry. Among these processing features is the vulcanization of the rubber mixture by means well known in the art. In this respect various changes in the processing of rubber formulations have been adopted to facilitate the aforesaid processing, thereby improving the properties of the rubber products. When the rubber mixtures contain vulcanizing agents such as sulfur and accelerators, a certain amount of premature vulcanization, which is known in the trade as scorching, may occur prior to the proper vulcanization. In addition, other compounds may also be present in the rubber formulation which will also adversely effect the induction time or scorch duration period prior to vulcanization. For example, the rubber formulation may contain an antiozonant therein in order to impart protection to the finished rubber product against ozone cracking. Among the more popular antiozonants which are utilized for this purpose are the phenylenediamine type of compounds. However, this type of antiozonant appears to promote scorching or premature vulcanization. Another material which may be present and which may have an adverse effect on the vulcanization period is a high pH furnace black which appears to lack the inherent inhibiting effect of the acidic channel blacks. In the past, it has been a common practice to utilize certain compounds to reduce the risk of scorching prior to vulcanization. However, such compounds have been of limited success and ofttimes have caused undesirable properties in the finished products.
In contrast to this, it has now been found that novel compounds comprising additional thiophosphoramides in which two of the substituents on the nitrogen atom comprise aryl, cycloalkyl, thioaryl, or thiocycloalkyl radicals may be utilized as vulcanization inhibitors in rubber formulations to allow control of premature scorch yet will afford products which do not exhibit the unwanted characteristics of rubber formulations containing other vulcanization inhibitors which have been used in the past. With respect to the novel substituted thiophosphoramides, the prior art has disclosed compounds which are similar in nature, yet do not possess the configuration of the novel compounds of the present invention. For example, German Patent No. 1,022,587 discloses substituted thiophosphoramides in which all of the substituents on the phosphorus atom contain alkyl radicals, there being two alkoxy radicals attached to the phosphorus atom and only one disubstituted nitrogen atom. However, this patent does not teach nor suggest the novel compounds of the type hereinafter set forth in greater detail, nor does the patent disclose that these compounds may be utilized as inhibitors against the premature vulcanization of rubber formulations. While other prior art references such as U.S. Pat. No. 2,957,020 have disclosed the equivalency of aryl or cycloalkyl radicals with alkyl radicals, there is no teaching of equivalency of alkyl, cycloalkyl and aryl radicals for the particular purpose of producing compounds which are effective inhibitors against the premature vulcanization of rubber.
The novel compounds of the present invention are specifically limited to compounds in which an alkoxy group is attached to a phosphorus atom while aryl or cycloalkyl radicals are attached to both the nitrogen and sulfur atoms of the compound. As will hereinafter be shown in greater detail, these novel compounds possess a specific utility in their ability to act as inhibitors against the premature vulcanization of rubber formulations.
This invention relates to novel compounds comprising substituted thiophosphoramides, and particularly to the use of these compounds as scorch inhibitors in the accelerated sulfur vulcanization of rubber formulations. More specifically the invention is directed to novel compounds comprising substituted thiophosphoramides in which the radicals on the nitrogen and sulfur atoms of the compound comprise either aryl or cycloalkyl radicals.
It is therefore an object of this invention to provide novel compounds of the type hereinafter set forth in greater detail, these compounds being useful as scorch inhibitors.
In one aspect an embodiment of this invention resides in a compound having the generic formula: ##STR1## in which R is an alkyl radical of from 1 to 6 carbon atoms, R' and R" are phenyl or cycloalkyl radicals containing from 4 to about 8 carbon atoms and n is an integer of from 1 to 2.
A specific embodiment of this invention is found in a novel compound comprising N-cyclohexylthio-N-phenyldiethylphosphoramide.